They have a general metric for it: > An ad is counted as viewable if at least 50% of its area is visible for at least 1 second for display ads, or at least 2 s

They have a general metric for it: > An ad is counted as viewable if at least 50% of its area is visible for at least 1 second for display ads, or at least 2 seconds for video ads. https://support.google.com/google-ads/answer/7029393?hl=en https://support.google.com/google-ads/answer/7029393?hl=en